Despite intensive efforts, the primary mechanism(s) responsible for the pathogenesis of essential hypertension remain unknown. The knowledge that a large fraction of the populations' variation in blood pressure is genetically determined suggests the possibility of identifying the genetic variants which directly contribute to the pathogenesis of hypertension. Subdividing hypertensive patients by using intermediate phenotypes - traits which are found to be present in some, but not all, hypertensive subjects - has the potential to increase substantially the power of such genetic approaches. There are five aspects to this proposal. First, in the routine use of the "intermediate phenotype" to subgroup our hypertensive patients and thereby increase the likelihood of linking the consequent pathophysiology to (a) specific gene(s). Second, are the state-of-the-art clinical research facilities - General Clinical Research Centers (GCRCs) - in which to perform the detailed physiologic protocols. Third, they will concentrate on using association analysis of candidate genes with expression of intermediate phenotypes of hypertensive in subjects off medications, while continuing to use the techniques of affected sibling pairs and family linkage analyses. Fourth, is the documentation of genetic epistasis in this population when sub- grouped by intermediate phenotype. Thus, they expect to be able to tease out the polygenes contributing to hypertension and subsequently investigate how they interact with each other and with environmental factors. Finally, there are a large number of subjects who have already been studied. In total, we have DNA, demographic data, clinical data, and some biochemical data from over 2400 individuals belonging to 1215 pedigrees who were examined to qualify subjects for the inpatient GCRC studies. Those who have undergone our intensive intermediate phenotyping protocol include 91 individuals from 15 pedigrees, 145 sibships of two or more hypertensive siblings (193 sibling pairs), 175 hypertensive "singletons" and 79 normotensive "singleton". The overall objectives of this project are threefold: 1) to determine if the four potential intermediate phenotypes are associated with each other; 2) to identify the gene(s) associated and/or linked to these intermediate phenotypes; and 3) to determine the likelihood of genotype predicting phenotype for increased specificity for prevention and/or intervention.